This invention relates to a method of protecting wooden objects, particularly elongate ground contact objects such as fence posts and telephone and electricity poles, from decay.
Preservative treated fence posts despite advances in preservative technology are still prone to ground level decay. Typically, after 20 years service, 5%-30% of posts will be showing signs of decay at or below ground level, although this is to some extent dependent on ground conditions and standards of preservative treatment.
This is unfortunate as the other parts of the posts, i.e. those deep below ground and those well above ground, would give a typical life of 40-50 years or more.
The top portion of a fence post, i.e. that from approximately 50-75 mm above ground level, is exposed to natural air flow and sunlight which will ensure a typical moisture content of 15%-70%, dependent on weather conditions. These factors combined with preservative treatment should mean that decay is very rare.
The bottom portion of the post, i.e. that from approximately 300 mm below ground level, does not decay because of the very high moisture content (typically 30%-90%) and the compacted wet soil conditions will ensure minimum levels of oxygen which is vital for the growth of rotting organisms.
This leaves the middle portion from about 300 mm below ground level to about 75 mm above ground level where conditions are ideal for decay.
The fence post acts as a wick drawing up water and solids to a band at ground level where the water evaporates. This portion of the post is very damp, typically 30%-90% moisture content, and is exposed to ground and airborne micro-organism which come into contact with the post and form primary moulds which are then followed by soft rots and Basidiomycetes.
Although preservatives greatly extend the life of fence posts (untreated posts typically last only 3-4 years), it is difficult to measure the standard of preservative treatment. Consequently, poor treatment can pass unnoticed.
Preservative belts, sleeves and wraps are also known. These relatively expensive products are predominantly used for the treatment of posts and poles in service, where their main purpose is to provide preservative material to replace that which may have been lost due to, inter alia, leaching. The sleeve wrap or belt provides additional preservative material at the outer face of the pole or post which is then absorbed, the objective being to totally penetrate the pole or post with preservative, hence eliminating decay.
GB-A-2297984 describes a method of protecting wooden objects from decay, the method comprising the step of applying a flexible outer barrier layer to at least that part of the object most vulnerable to decay, providing a bituminous substance between the barrier layer and the object and heating the barrier layer so as to melt the bituminous substance sufficiently for it to bond intimately to the wooden object. The barrier layer is in the form of heat shrinkable plastics material and is formed into, or is in the form of, a sleeve which is heat shrunk onto the object.
When applying the sleeve to smooth circular posts or poles using infra-red, or hot air, heating to heat shrink the sleeve onto the object, an excellent uniform bond is achieved between the bitumen and the post face. This bond is essential for the sleeve to work effectively.
However, it has been found that when the sleeve is heat shrunk onto square or other non-circular posts, the bitumen does not form a satisfactory seal. The present invention seeks to overcome this problem.